SXR500 Runs terrible when hot

J

Jsrx700

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Oct 20, 2012
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Age
56
Location
Manotick
I'm the original owner of a 2000 Sxr500, it developed a problem just after the warranty expired. After running hard for 10 - 15 minutes the engine begins to lose power demanding more and more throttle until eventually bogging down to 30 MPH wide open. After a 5 minute stop, it takes off like normal then the problem repeats. Sled is extremely hard an fuel and oil. Carbs have been serviced religiously, clutches tuned, reed valves installed last year. TORS problem ruled out. The odd thing is that the problem has not worsened over the years as one would expect if there was an engine or electrical problem. I'm wondering about the stator, perhaps it's got some weird issue when it heats up. One thing on the back of my mind is the reverse kit that the dealer sold me with the machine, I installed it. It wasn't too long after that that the problem began.....could a gearing problem behave this way? Any advice would be appreciated. Three Yamaha dealers have had a go at this one, no success yet. Thanks
 
I'm planning on taking some resistance readings cold and hot, should the values vary normally? Would the headlight not dim in conjunction with the loss of power if the stator was at fault or is there a separate lighting coil?
 
Maybe I miss read post but head light works fine right? This wouldnt rule out stator, I dont think. To be completely honest not that familar with the twins. I am thinking the tripples had issues with harness rub threws. I would definately suspect electronics over any gearing/ chain case issue's. My brother in law had similar problems with a phazer, His issue ending up being CDI.
 
Something on the brake assy. isn't seizing up is it? Next time it boggs down like that, feel your chaincase and brake assy. on it. Is it smoking hot? Maybe you put a collar or bushing in backwards? Check the jackshaft, secondary, primary for excess heat. If you run it on a stand, does it still act up like this?
 
Thanks everyone, great advice. To clarify the headlight is not effected. The brake and chaincase housing do not seem any warmer that the other sleds we're running with, nor does the machine feel as though there is any abnormal resistance during deceleration or while decending a hill. It takes so long for the problem to occur sometimes, hard to troubleshoot during the off season when you'd like to work on it. I suppose running it on the stand for a half hour could help isolate electrical vs drive issue.
 
I've seen coils act similar to that when they crap out and start breaking down. Maybe an inline tester?
 
FJViper said:
I've seen coils act similar to that when they crap out and start breaking down. Maybe an inline tester?
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Definately. When the insulation that is compromised (in the coil) gets hot, the insulating value takes a nose dive and the power to the spark plug goes to sh!t.Everything will work perfectly fine until the temperature under the hood gets up to ??? degrees and causes problems w/ the faulty coil.
Once it starts to act up, pull the plug wires one at a time (w/ insulated pliers) to troubleshoot which coil is AFU.
 
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A couple of bucks said:
Definately. When the insulation that is compromised (in the coil) gets hot, the insulating value takes a nose dive and the power to the spark plug goes to sh!t.Everything will work perfectly fine until the temperature under the hood gets up to ??? degrees and causes problems w/ the faulty coil.
Once it starts to act up, pull the plug wires one at a time (w/ insulated pliers) to troubleshoot which coil is AFU.
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Pulling a plug wire on a running sled (essentially un-grounding it) will eventually cause a breakdown in the coil insulation and often create such intermittent/heat related issues. Depending on RPM, that's 1000's of volts wanting to go somewhere and they'll eventually find a way to ground.

I'd recommend shutting it off, install an old plug on the disconnected high tension lead and ground it. Or make an extension that exposes the cap of the spark plug and use a 12 volt test light attached to ground to ground the plug. A piece of 1/4" steel tubing about 2" long that'll sit on the plug cap and insert into the wire end cap works well. Just touch the pointed end of your test light to the tube when performing a power balance.

At the very least if you pull the wire when running get the plug cap to a ground ASAP. Undestand though, you've just gone from a .020"-.030" plug gap to .500" or larger gap the spark has to jump so you're still taxing the secondary beyond it's design.
 
snomofo said:
Pulling a plug wire on a running sled (essentially un-grounding it) will eventually cause a breakdown in the coil insulation and often create such intermittent/heat related issues. Depending on RPM, that's 1000's of volts wanting to go somewhere and they'll eventually find a way to ground.
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Shoot....that's right. Sorry about that bad advise.
 
A couple of bucks said:
Shoot....that's right. Sorry about that bad advise.
Click to expand...


I should have said I've done it many times over the years myself... without causing a problem, until I did.

I keep a few pieces of stainless tube cut to about 2" length in my box to act as a post between the spark plug tip and wire cap. I then ground each post/cylinder with a 12 volt test light when checking cylinder power balance.
 
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